Americans by 48-41 percent hold an unfavorable opinion of Islam – its highest unfavorable rating in ABC/Post polls since 2001. And 29 percent expressed the belief that mainstream Islam encourages violence against non-Muslims – double what it was early in 2002.

Unfamiliarity is a central factor in these views. Fifty-five percent of Americans concede that they lack a good basic understanding of Islam; about as many, 53 percent, don’t personally know a Muslim.

Perceptions of Islam as a peaceful faith are the highest among non-religious Americans, with about two-thirds holding that view. Among Catholics, 60 percent see mainstream Islam as a peaceful faith; it is 55 percent among all Protestants, but drops to 48 percent among white evangelical Protestants.

There are deep divisions in perceptions of Islam between younger and older Americans as well: More than six in 10 younger than 65 said Islam is a peaceful religion, but that drops to 39 percent among seniors.

Republicans are also more apt than others to hold negative attitudes toward Islam, with six in 10 having unfavorable views, compared with about four in 10 for Democrats and independents. Among conservative Republicans, 65 percent view Islam unfavorably; liberal Democrats, in contrast, are 60 percent positive.

This partisan divide is also apparent on the question of whether mainstream Islam encourages hostility toward non-Muslims, with Republicans about twice as likely as Democrats to say it does. Nearly half of conservative Republicans see centrist Islam as a promoter of violence.

The polls found that those who profess an understanding of Islam, or know a Muslim, have much more positive views of the religion.

This may be why President Obama said in Turkey: “The Untied States has been enriched by Muslim-Americans. Many other Americans have Muslims in their family, or have lived in a Muslim-majority country. I know, because I am one of them.”

The line was a bold one for Obama, who has been falsely accused of being Muslim. The claim persists on some right-right websites, which now may try to twist his remarks as proof.

Obama’s Kenyan father and grandfather were Muslims, and he spent time as a child in Indonesia, the country with the world’s largest Muslim population.

But other factors also are at play, and negative views of Islam remain the same even amongst those who say they have become more familiar with the religion.

Forty-five percent now feel they basically understand the religion, 5 points above its previous high and 20 points above its low in 2002. And the 47 percent who know a Muslim is up from 41 percent in October 2001.